PROJECT SUMMARY Goal: We propose to utilize a series of novel human iPSC-based cardiac microphysiological systems of increasing complexity to investigate the hypothesis that maturation of dystrophic cardiomyocytes is necessary to elucidate correct disease phenotype development in vitro. The aim is to create a multifaceted screening system using several core technologies developed by our group to evaluate different aspects of myocardial electromechanical function. We have developed the ability to engineer pluripotent stem cells from patient urine, enabling non-invasive cell sampling from human subjects. Furthermore, we have collected preliminary data demonstrating that application of combinatorial maturation stimuli to healthy and dystrophin-null cardiomyocytes helps stratify the disease phenotype. Based on these achievements, we posit that the use of a targeted set of functional assays in combination with appropriate maturation stimuli will provide a more comprehensive understanding of disease progression in muscular dystrophy. Focus/Aim: Our proposed research focuses on the use of techniques with the potential to act synergistically to enhance cardiac phenotype development in stem cell-derived cardiomyocytes through manipulation of different cellular mechanisms. Specifically, we will investigate the effect of structural organization by nanopatterned substrates, nuclear receptor signaling by thyroid hormone, and alterations in metabolic signaling pathways by Let-7 microRNA over-expression on the development of healthy cardiomyocytes and their dystrophin-null counterparts created using CRISPR-Cas9 gene editing technology. Nanotopographic microelectrode arrays will be used to evaluate electrophysiological function (Aim 1), while nanopatterned cell sheet stacking technology will be used to create 3D cardiac patches for analyzing contractile function (Aim 2) as well as organized 3D ventricle structures for assessing pressure generation and stroke volume (Aim 3). Each of these systems will be used to evaluate a panel of drugs for their potential to ameliorate the dystrophic phenotype. The compounds chosen for this study target a range of metabolic, structural, and signaling pathways known to be associated with different aspects of muscular dystrophy pathology. The analysis of multiple functional endpoints for each compound will therefore provide more comprehensive information on the likely effect of drugs when administered to human patients. The movement from platforms with higher levels of throughput to those with higher degrees of biomimicry, as the work transitions from Aim 1 to Aim 3, constitutes a natural ?funneling? of the drug screening process. Candidates identified using simpler multiplexed models will be re- evaluated using systems that offer closer representations of the native tissue, and provide physiological endpoints analogous to those monitored in patients. As such, the proposed method for studying maturation and dystrophic phenotype development could provide the framework for a next generation screening process geared towards replacing animal testing with increasingly physiologically representative models of the myocardium.